In internal combustion engines, camshafts are used to actuate the so-called gas exchange valves. The cams of the camshafts usually rest against cam followers. When a camshaft is set in rotation, the cams thus roll against the cam followers, which in turn actuate the gas exchange valves. The angular shift of the camshaft relative to a crankshaft in order to achieve optimized control times for different speeds and load states is referred to as camshaft adjustment. One design variant of a camshaft adjuster operates, for example, according to the known swivel motor principle.
The camshaft adjuster is in this case mounted fixedly on the camshaft. A central valve controls the exchange of oil between the camshaft adjuster and the oil circuit of the internal combustion engine. The access openings and/or the outlets of the central valve are formed in a central valve housing. A control piston is guided in an interior of the central valve housing. The control piston is designed as a cylindrical body having a cavity. The control piston is coupled to an electromagnet by way of a thrust pin, the electromagnet being configured to move the control piston axially in the central valve housing. This is described, for example, in German unexamined publications DE 10 2011 080 421 A1, DE 10 2010 050 813 A1 and DE 10 2006 027 349 A1.
In the known central valve applications, attempts are made to install the two sliding partners, i.e., the thrust pin and the control piston, without any offset. A contact surface between the control piston and the thrust pin is thus formed in a centric manner on the control piston of the central valve. Due to this centric or slightly eccentric (within the scope of the permissible positional deviation) alignment of the two sliding partners, no relative movement (in the case of a centric position) or only a slight relative movement occurs between the control piston and the thrust pin. During the arising relative movement, the control piston rotates and the thrust pin is stationary. The low or lacking sliding speed of the sliding partners relative to one another prevents or hinders the buildup of a stable hydrodynamic lubricating film and thus fosters wear on the sliding pairing due to a lack of lubrication and increased friction. Dry friction thus occurs, whereby in particular the surface roughness of the control piston results in wear of the thrust pin.